1. Field of the Invention
The present invention is broadly concerned with an improved splash-type fill bar used in the fill assemblies of evaporative water cooling towers to enhance the performance thereof. More particularly, it is concerned with such an improved fill bar which is somewhat trapezoidally shaped in cross-section and presents an uppermost flat, relatively wide top wall, together with a pair of outwardly diverging, obliquely oriented sidewalls and a corresponding pair of laterally extending, side marginal flange walls extending from the lower edge of each sidewall; the top and sidewalls of the splash fill bar are apertured, whereas the flange walls are imperforate. Comparative tests using the fill bars of the present invention versus commercially available bars of inverted V configuration demonstrate that the bars hereof give enhanced tower performance.
2. Description of the Prior Art
In general, evaporative water cooling towers include an upper hot water distribution system such as an apertured distribution basin or the like, and a lowermost cold water collection basin. Commonly, a splash-type water dispersing fill structure is disposed in the spaced between the hot water distribution system and the underlying cold water collection basin. Such fill structure includes a plurality of elongated, horizontally arranged and staggered splash bars supported at spaced intervals by an upright grid structure. Hot water discharged from the distribution pan falls onto the bars and disperses, forming droplets to facilitate the cooling process. At the same time, cooling air currents are drawn through the fill structure, either by means of a motor driven fan or through use of a natural draft-inducing hyperbolic tower.
The fill structure of a given tower is often regarded as the single most important component, because the fill promotes interactive thermal interchange between the water and air. As water droplets are discharged from the distribution pan, the temperature difference between the relatively warm water and the cooling air causes evaporation on the surface of the droplets and cooling of the water occurs therefore at a rapid rate. However, as the surface temperature of individual droplets approaches the wet bulb temperature of the surrounding air, the cooling process is diminished and is dependent upon the rate of heat transfer from the inside of the droplet to the outside of the surface thereof. As such, it is desirable to interrupt the fall of individual droplets by splashing the drops on a fill bar, thus instantly exposing new water surfaces and, in some cases, subdividing the droplets into smaller droplets to increase the total water surface area available for exposure to the passing air.
As can be appreciated, the characteristics of any fill structure splash bar must meet several criteria to assure satisfactory operation and performance. First, the splash bar should provide consistent, predictable dispersal and breakup of the water droplets over a range of water loadings typically encountered in practice. Preferably, the descending droplets are uniformly broken into relatively fine particles in a widely divergent pattern to facilitate enhancement of the cooling process. However, formation of a fine mist should be avoided, inasmuch as such mists can be readily entrained in the cooling air currents, and thus discharged to the atmosphere unless further steps are taken. Moreover, splash bar structure should cause a minimum amount of air pressure drop in order to keep fan horsepower requirements and operating costs at relatively low levels. Additionally, a splash bar structure should have sufficient structural strength to span the distance between adjacent upright grid supports, since deflection of the bars can enable the water to channel toward the low part of the bar, thereby causing coalescence of water and unequal water dispersal throughout the passing air streams. This problem of bar deflection is most common when the bars are formed of synthetic resin material, since such bars often lose strength and stiffness when subjected to the elevated temperatures of hot water to be cooled. Finally, cost is an important consideration in the selection and fabrication of splash bars. For example, a large hyperbolic induced-draft tower may utilize something on the order of 2,000,000 bars, each four feet in length. As a result, the use of bars formed of expensive metallic materials cannot usually be economically justified, even though metallic bars may provide very adequate performance.
Early splash bars were formed of wood species such as redwood or treated Douglas fir. However, wood splash bars, even when normally rot resistant, can deteriorate due to chemicals in the water stream. Also, wood bars present serious a fire hazard as soon as the water flow is interrupted and the moisture remaining on the bars has substantially evaporated.
It has also been proposed in the past to fabricate specialized bar configurations from synthetic resin materials. For example, U.S. Pat. No. 3,389,895 to DeFlon discloses various splash bar configurations, including those of inverted V configuration, and bars of inverted channel shape. The V-type bars described in this patent have achieved a measure of commercial usage, although they are relatively expensive. On the other hand, the inverted channel-shaped bars described in the '895 patent (see FIG. 5) are plagued with serious operational deficiencies. Specifically, such bars, because of the presence of upright, vertical sidewalls, tend to create coalesced streams or sheets of water which are inimical to tower performance. Therefore, these splash bars had achieved little, if any, commercial success.
U.S. Pat. No. 3,647,191 to Fordyce describes a splash fill bar of somewhat M-shaped configuration, presenting an apertured, V-shaped top wall presenting a pair of inclined wall sections, together with upright, imperforate sidewalls. This design has proved to be deficient in that descending hot water tends to collect in the central region of the top wall, thereby leading to unequal water distribution.